Aw now I feel bad, mihawk calls shanks a hasbeen, he know shanks is weaker than him, he gauge zoro strength and knew it was way weaker than he was, fuji said luffy has the strength to back up his words, Mihawk doesn't know shanks full power, or zoro, fujitora doesn't know luffy but they can gauge it and tell
It's not that hard to understand its that simple, Mihawk knew WB was stronger than him despite not knowing his full strength